1. Technical Field
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a liquid crystal display (LCD) device, in which incomplete dispensation of liquid crystal, gravity defects and foreign material generated internally are mitigated by forming column spacers that maintain a cell gap in an active region and a honeycomb-shaped arrangement of column spacers in a margin region.
2. Related Art
As the demand for various display devices increases, development of various types of flat display devices, such as LCD devices, plasma display panel (PDP) devices, electroluminescent display (ELD) devices, and vacuum fluorescent display (VFD) devices, has increased. Among these various flat display devices, LCD devices have been used commonly because of their thin profile, light weight, and low power consumption. LCD devices are used commonly as a substitute for cathode ray tube (CRT) devices. In addition, LCD devices are used commonly in notebook computers, computer monitors, and televisions. However, to use LCD devices as general display devices in a large sized screen, it is desirable to display images having high resolution and luminance in addition to maintaining the light weight and thin profile and low power consumption of the overall device.
In LCD devices, different types of spacers are used to maintain the cell gap between the substrates forming the LCD device. Depending on the method of fabrication, these spacers are spherical or columnar. The spherical spacers are added after the substrates are fabricated and the column spacers are provided during fabrication of one of the substrates. The column spacers are formed in specific portions of the LCD device and the spherical spacers are free moving and are randomly scattered throughout the LCD device.
Spherical spacers are used when forming the LCD panel using an injection method in which the substrates are fabricated and then liquid crystal injected into the cavity therebetween. However, this method requires significant amounts of time to inject the liquid crystal material, thereby lowering production yield. It is also difficult to completely inject the liquid crystal material when forming large LCD devices. In addition, as several liquid crystal injection devices are filled at the same time due to the complicated process and the considerable process time involved, a large space is required.
In a liquid crystal dispensing method, two substrates are bonded to each other after dispensing liquid crystal material on one of the substrates. Spherical spacers cannot be used to maintain the cell gap in this method as the spherical spacers move along a dispensing direction of the liquid crystal material. Instead, column spacers fixed to the substrate maintain the cell gap. However, the use column spacers engender problems not encountered by spherical spacers.
FIG. 1A is a schematic cross sectional view of a color filter substrate on which a column spacer is fabricated. FIG. 1B is a schematic cross sectional view of the bonding state of the TFT substrate and the color filter substrate. FIG. 1A shows the column spacers 20 formed on the color filter substrate 2. Each column spacer 20 has a height h. As shown in FIG. 1B, when the color filter substrate 2 is bonded to the TFT substrate 1 on which liquid crystal is dispersed, the height (h) of the column spacer 20 is decreased to (h′), which corresponds to the cell gap. This difference in thickness (h-h′) is defined as the gravity margin.
As can be seen, the contact area between the column spacers and the relatively flat TFT substrate is relatively large, making it hard to obtain the gravity margin (h-h′). Also, if the LCD device is maintained at a high temperature, a protruding portion may develop due to expansion of the liquid crystal, making it harder to obtain the gravity margin. Moreover, if the LCD panel is placed in a vertical direction for an extended period of time, such as when the LCD panel is used for a television monitor, gravity causes the liquid crystal molecules to move to a lower portion of the panel, creating a protruding portion and also making it harder to obtain the gravity margin. As a result, if an excessive amount of the liquid crystal is provided or the liquid crystal is maintained at a high temperature or the LCD device is tilted, a gravity defect may exist.
Further, the large contact areas generate large frictional forces when the substrates move relative to each other. The frictional forces prevent restoration of the liquid crystal molecules to the original state and generate long-lasting spots on the screen of the LCD device. This is shown more graphically in FIG. 2A and FIG. 2B, which are cross sectional and plane views of a portion having touch spots in a conventional LCD device.
As described above and shown in these figures, when the LCD panel 10 is continuously touched with a finger along a particular direction, the upper substrate of the LCD panel is shifted by an amount along the touch direction. The liquid crystal molecules between the column spacers 20 are not restored to their original states, thereby generating spots on the screen. In addition, when the LCD panel is touched, as shown in FIG. 2B, the liquid crystal molecules gather around the touched portion causing the region around the touched portion to protrude. In this case, the cell gap “h1” corresponding to the protruding portion is higher than the cell gap “h2” of the remaining portion, thereby causing light leakage due to irregular alignment of the liquid crystal molecules. Additionally, since the touched portion has a decreased amount of liquid crystal molecules, blurred portions appear on the screen in a black state, thereby deteriorating luminance of the LCD panel 10. Furthermore, if the LCD panel is pressed at a portion in which column spacers are not present, the substrates bend and form a hollow state due to low restoring speed of the substrates, thereby generating spots on the screen of the LCD panel.
When an external force is applied to the screen of the LCD device, the liquid crystal molecules are displaced from an active region, in which images are displayed, to a liquid crystal margin region, in which images are not displayed. This causes incomplete dispensation of the liquid crystal in the active region and thus, black spots to appear on the screen. Even if a dam is present between the active region and the liquid crystal margin region to contain the liquid crystal molecules after they have migrated and the external force is removed or the temperature restored to the ambient temperature, the liquid crystal molecules are not entirely restored to the active region. Moreover, shifting of the column spacer due to application of the external force causes peeling at the contact portion of the alignment layer of the TFT substrate and the column spacer. This peeling generates foreign material, which is then dispersed throughout the active region.